This invention relates in general to aircraft lift augmentation systems and, more particular to a system using plural powered rotors parallel to the trailing edge of an aircraft wing.
Conventional aircraft generally have gas turbine engines or internal combustion engines either driving propellers or using direct thrust oriented substantially parallel to the wings, with the engines located in the nose of the fuselage or in or below the wings or adjacent to the aft of the fuselage. Because they must rely on the speed of the air over the wing surface to produce lift these aircraft tend to require long runways for landing and takeoff, especially when heavily loaded.
Helicopters use horizontally rotating airfoils to permit vertical takeoff and hovering. While having the ability to land and takeoff from very small areas, helicopters tend to have relatively low load carrying capacity.
A number of different aircraft have been designed in attempts to combine the load carrying capabilities of conventional aircraft and the vertical, or short distance, takeoff and landing abilities of helicopters. Among these are aircraft in which engines and propellers can be tilted between vertical and forward orientation, so that the aircraft can take off vertically or over a short distance with the propellers rotating in a substantially horizontal plane. The engines can then be rotated to bring the propellers into a conventional vertical plane during flight. Other similar aircraft tilt the entire wing carrying the engines and propellers between positions providing vertical and forward propulsion. While effective on a limited basis, these aircraft are often difficult to fly during the transition between vertical and horizontal flight, and tend to be heavy and have low payloads due to limitations in the vertical lift capabilities. These systems include engine on each side of the fuselage, each driving a large diameter propeller. A cross shaft must be provided between the engines to balance engine operation and allow one engine to drive both propellers in the event of failure of one engine. The cross shaft system is very heavy but necessary since, obviously, loss of thrust from one propeller would be catastrophic.
A system that combines conventional axial tractor engines and a horizontally rotating, helicopter-like, rotor inset into the center of the aft edge of a semi-circular aircraft wing above the fuselage is disclosed by Malvestuto in U.S. Pat. No. 3,372,891. This design has proven to be less than fully effective primarily due to the inefficient semi-circular wing, the single rotor, the lack of attitude control for the rotor and the above-fuselage location that distorts the pattern of downward rotor air flow.
Small aircraft, such as close support attack aircraft, have been provided with ducts directing jet engine flow in vertical or near vertical directions to provide vertical takeoff and landing capability, or short distance takeoff capability when heavily loaded. Again, aircraft control while transitioning between vertical and horizontal flight is difficult. The ducts and duct operating system tend to be heavy and complex, limiting the carrying and operational capacities of the aircraft and result in less than desired reliability.
A number of wing lift augmentation systems have been designed to increase wing lift at low speeds to permit short takeoff and landing capabilities. These include very large flaps, slots or leading edge extensions, various airflow deflector concepts and methods of blowing air over various wing surfaces. These systems depend on fine and precise control over jet sheets of air over the wing surfaces. This fine control is difficult to control under varying conditions in practice.
Thus, there is a continuing need for improvements in aircraft and aircraft propulsion lift systems to permit safe and reliable short takeoff and landing characteristics without significantly adversely affecting the operating characteristics of the aircraft or its load carrying capacity and which permits operation of the aircraft in a normal manner with the lift augmentation system disabled.